The present invention relates to a coaxial cavity resonator. The invention also relates to a filter and a use of a resonator component in a filter.
Coaxial cavity resonators are widely used in telecommunication applications. It has been the aim of research and development to achieve smaller resonators and, at the same time, maintain or increase the Q-value of the resonators, i.e. increase the Q-value per volume.
A simplest type of coaxial cavity resonator comprises a rod, having a length of a quarter wavelength (xcex/4), arranged inside a cavity, so called rod resonator. A first end of the rod is connected to the bottom wall of the cavity and the second end of the rod is in open-circuit relation to the cavity walls. To obtain a reasonable good Q-value, the cross-sectional diameter of the cavity should be approximately 3 times the diameter of the rod.
The most common way of attaching said rod to the bottom wall is by soldering. This manufacturing technique has the drawback of introducing a damaged surface at the joint, and thereby decreasing the Q-value of the resonator. Another drawback is difficulties in aligning the rod during assembly of the resonator.
Additional problem is coating of interior walls of cavity necessary to receive a high Q-value.
In European patent application EP 0 964 473, a filter is disclosed, see FIG. 1, which provides a cavity made from a material having a good electrical conductivity with integrated resonator bodies. By making the resonators from the same piece of material as the cavity walls, undesired effects at the joint between each resonator and the cavity wall can be avoided since there is no interfaces between them.
A drawback with the filter is that it is very expensive to manufacture. Another drawback is that it is not very flexible, since a new mold is required when manufacturing new filter having less or more resonators.
According to an aspect of the present invention there is provided a coaxial cavity resonator as specified by the coaxial cavity resonator including walls delimiting a cavity, and at least one resonator body including a conductive rod having a first end being in short circuit relation to a first wall of the cavity walls. The first end has a cross-sectional area. A first conductive supportive plate has a first side connected to the first end of each rod. The first side has a greater area than the cross-sectional area of the first end of the rod. A second side, opposite the first side of the supportive plate, is electrically connected to the first wall. A retainer is provided in the first cavity wall to guide the supportive plate. An attachment is provided to secure the first supportive plate to the retainer, and the supportive plate and at least a portion of the rod closest to the first end have a continuous conductive surface with high conductivity.
The present invention is also directed to a filter in which at least one of the described coaxial cavity resonator is mounted as specified in the filter and comprises conductive outer walls, an input and an output, and at least one resonator.
The invention is also directed to the use of a resonator component in a filter where the component forms a part of the inside of at least one cavity wall. The component comprises a conductive rod having a first end. The first end has a cross-sectional area. A first conductive supportive plate has a first side connected to the first end of the rod. The first side has a larger area than the cross-sectional area of the first end of the rod. A second side, opposite the first side of the supportive plate, is electrically connectable to a cavity wall of the filter, and the supportive plate and at least a portion of the rod closest to the first end have a continuous conductive surface having high conductivity.
An advantage with the present invention is that the resonator body is easier to align during manufacture.
Another advantage with the present invention is that the resonators are easy to assembly, since they can be made of relatively few parts.
Another advantage is that the present invention is cheap to manufacture.